The United States has warned its citizens living in Nigeria that Islamist sect Boko Haram is planning attacks on the capital Abuja, including major hotels there.
Boko Haram, which wants sharia, Islamic law, more widely applied across Africa's most populous nation, has killed hundreds in gun and bomb attacks this year.
The U.S. Embassy has received information that Boko Haram may be planning attacks in Abuja, Nigeria, including against hotels frequently visited by Westerners, an emergency message on its website said on Wednesday.
The Nigerian government is aware of the threat and is actively implementing security measures.
The U.S. authorities issued a similar warning in November, naming the Hilton, Sheraton and Nicon Luxury as Abuja hotels that could be targets for Boko Haram, but it later retracted it.
Nigerian authorities said then that high profile hotels were always a possible target but security was tight and people should not live in fear. However, occupancy at those hotels dipped after the last U.S. warning.
The embassy did not name specific targets this time. The Hilton in Abuja said it always took security seriously.
Boko Haram strikes usually target police, authority figures and churches in the mostly Muslim north, although there have been a handful of deadly attacks in and around Abuja, which is home to the president's villa, government ministries and foreign embassies.
The sect claimed responsibility for a bombing at police headquarters in Abuja last year before a car bomb at the U.N. Nigeria headquarters in August killed 26 people.
The police said they killed one member of the sect and arrested 13 others on Tuesday during a crackdown in the sect's home base of Maiduguri, the capital of Borno state in the remote northeast on borders with Chad, Cameroon and Niger.
Boko Haram shot dead two people on Monday in Maiduguri, where it has carried out almost daily attacks in recent months.
President Goodluck Jonathan, who is a Christian from the southern oil-producing Niger Delta, has been criticised by Nigerians and foreign diplomats for not getting a grip on violence in the north, from where many feel he is detached.
A bomb near a church in northern city Kaduna on Easter Sunday killed over 30 people but Jonathan was on holiday in Abuja and his team declined to make any comment.
Boko Haram's purported leader, Abubakar Shekau, has appeared in two al Qaeda style videos posted on the Internet this year but has made only vague threats and no clear demands.
He said his main objective was to spread Islamic law, free its imprisoned members and kill infidels who were working against it, whether Christian or Muslim.
Security experts believe Shekau is likely the leader of the main faction of the sect based in Maiduguri, which typically targets the police who killed its members, prisons and kills religious figures who speak out against its insurgency.
There are several factions within Boko Haram spread across the north and some have loose ties with Islamist groups outside the country, including al Qaeda in the Islamic Maghreb, security experts and Western diplomats say.
(Reporting by Joe Brock; Editing by Tim Cocks)